Low vitamin intake tied to asthma risk

People with symptomatic asthma eat less fruit and consume less
vitamin C and manganese than people who don't have the disease, a
new study shows.

The findings suggest that "diet may be a potentially modifiable
risk factor for the development of asthma," Dr N.J. Wareham of the
Medical Research Council in Cambridge, UK and colleagues write in
the medical journal Thorax.

Several antioxidant nutrients have been linked to reduced asthma
risk, Wareham and his team note, but it is not clear whether each
of these nutrients plays a role in reducing risk or if they instead
represent an overall healthier lifestyle.

To investigate, they compared the diets of 515 adults who had
been diagnosed with asthma and 515 "controls" - similar adults
without the disease. All reported their food intake over a one-week
period. One-third of the asthma patients reported having had no
symptoms in the past 12 months.

Asthma patients ate an average of 132.1 grams of fruit daily,
compared to 149.1 grams for healthy controls. Those who ate at
least 46.3 grams of citrus daily had about half the risk of having
asthma with symptoms compared to those who ate no citrus fruit at
all. Lower intake of both vitamin C and manganese were tied to an
increased risk of symptomatic asthma, while symptomatic asthma
patients had significantly lower levels of plasma vitamin C than
healthy controls.

The findings don't support the idea that overall healthy
lifestyle plays a role in asthma risk, the researchers note,
because both asthma patients and healthy controls consumed the same
amounts of calories and fat and showed similar levels of physical
activity, education, and likelihood of having smoked in the
past.

While it appears clear that lower vitamin C levels among asthma
patients are due to lower fruit intake, it isn't clear what dietary
factors contribute to reduced manganese consumption, they add.
Controls did not eat more cereals and grains - both of which are
rich in manganese - than asthma patients, although they did drink
more tea, which is another key source of the antioxidant
nutrient.

The researchers conclude: "These findings may be of public
health importance in understanding the apparent increase in the
prevalence of asthma."